1. Field of the Invention
The present invention relates generally to a method and an apparatus for configuring content in a broadcast system, and more particularly, to a method and an apparatus for configuring a data unit of content in a broadcast system supporting multimedia services based on an Internet Protocol (IP).
2. Description of the Related Art
A conventional broadcast network generally uses the Moving Picture Experts Group-2 Transport Stream (MPEG-2 TS) for transmission of multimedia content. The MPEG-2 TS is a representative transmission technique that allows a plurality of broadcast programs (a plurality of encoded video bit streams) to transmit multiplexed bit streams in a transmission environment having errors. For example, the MPEG-2 TS is appropriately used in digital TeleVsion (TV) broadcasting, etc.
FIG. 1 illustrates a layer structure supporting a conventional MPEG-2 TS.
Referring to FIG. 1, the conventional MPEG-2 TS layer includes a media coding layer 110, a sync (synchronization) layer 120, a delivery layer 130, a network layer 140, a data link layer 150, and a physical layer 160. The media coding layer 110 and the sync layer 120 configure media data to a format usable for recording or transmission. The delivery layer 130, the network layer 140, the data link layer 150, and the physical layer 160 configure a multimedia frame for recording or transmitting a data block having the format configured by the sync layer 120 in/to a separate recording medium. The configured multimedia frame is transmitted to a subscriber terminal, etc., through a predetermined network.
Accordingly, the sync layer 120 includes a fragment block 122 and an access unit 124, and the delivery layer 130 includes an MPEG-2 TS/MPEG-4 (MP4) Real-time Transport Protocol (RTP) Payload Format/File delivery over unidirectional transport (FLUTE) 132 block, an RTP/HyperText Transfer Protocol (HTTP) block 134, and a User Datagram Protocol (UDP)/Transmission Control Protocol (TCP) block 136.
However, the MPEG-2 TS has several limitations in supporting multimedia services. Specifically, the MPEG-2 TS has limitations of inefficient transmission due to unidirectional communication and a fixed size of a frame, generation of an unnecessary overhead due to the usage of a transport protocol, and an IP specialized for audio/video data, etc.
Accordingly, the newly proposed MPEG MEDIA Transport (MMT) standard has been proposed by MPEG in order to overcome the above-described limitations of the MPEG-2 TS.
For example, the MMT standard may be applied for the efficient transmission of complex content through heterogeneous networks. Here, the complex content includes a set of content having multimedia factors by a video/audio application, etc. The heterogeneous networks include networks in which a broadcast network and a communication network coexist.
In addition, the MMT standard attempts to define a transmission technique that is friendlier to an IP that is a basic technique in a transmission network for the multimedia services.
Accordingly, the MMT standard attempts to representatively provide efficient MPEG transmission techniques in a multimedia service environment that changes based on the IP, and in this respect, the standardization and continuous research of the MMT standard have been progressed.
FIG. 2 illustrates a conventional layer structure of an MMT system for transmission of a multimedia frame according to multi-service/content through heterogeneous networks.
Referring to FIG. 2, an MMT system for configuring and transmitting a multimedia frame includes a media coding layer 210, an encapsulation layer (Layer E) 220, delivery layers (Layer D) 230 and 290, a network layer 240, a data link layer 250, a physical layer 260, and control layers (Layer C) 270 and 280. The layers include three technique areas, Layer E 220, Layers D 230 and 290, and Layers C 270 and 280. Layer E 220 controls complex content generation, Layers D 230 and 290 control the transmission of the generated complex content through the heterogeneous network, and Layers C 270 and 280 control consumption management and the transmission management of the complex content.
Layer E 220 includes three layers, i.e., MMT E.3 222, MMT E.2 224, and MMT E.1 226. The MMT E.3 222 generates a fragment, which is a basic unit for the MMT service, based on coded multimedia data provided from the media coding layer 210. The MMT E.2 224 generates an Access Unit (AU) for the MMT service by using the fragment generated by the MMT E.3 222. The AU is the smallest data unit having a unique presentation time. The MMT E.1 226 combines or divides the AUs provided by the MMT E.2 224 to generate a format for generation, storage, and transmission of the complex content.
Layer D includes three layers, i.e., MMT D.1 232, MMT D.2 234, and MMT D.3 290. The MMT D.1 232 operates with an Application Protocol (AP) similarly functioning to the RTP or the HTTP, the MMT D.2 234 operates with a network layer protocol similarly functioning to the UDP or the TCP, and the MMT D.3 290 controls optimization between the layers included in Layer E 220 and the layers included in Layer D 230.
Layer C includes two layers, i.e., MMT C.1 270 and MMT C.2 280. The MMT C.1 270 provides information related to the generation and the consumption of the complex content, and the MMT C.2 280 provides information related to the transmission of the complex content.
FIG. 3 illustrates a conventional data transmission layer for a broadcast system.
Referring to FIG. 3, Layer E in a transmission side stores elements of the content, such as video and audio, encoded to a Network Abstraction Layer (NAL) unit, a fragment unit, etc., by a codec encoder, such as an Advanced Video Codec (AVC) and a Scalable Video Codec (SVC) in units of AUs in layer E3, which is the top-level layer, and transmits the stored elements in the units of AUs to layer E2, which is a lower layer.
In the conventional technique, a definition and a construction of the AU transmitted from Layer E3 to Layer E2 depend on a codec.
Layer E2 structuralizes a plurality of AUs, encapsulates the structuralized AUs based on Layer E2 units, stores the encapsulated AUs in the unit of Elementary Streams (ES), and transmits the stored AUs to Layer E1, which is a next lower layer. Layer E1 instructs a relation and a construction of the elements of the content, such as the video and audio, encapsulates the elements together with the ES, and transmits the encapsulated elements to Layer D1 in units of packages.
Layer D1 divides a received package in accordance with a form suitable for transmission of the divided package to a lower layer, and the lower layer then transmits the packet to a next lower layer.
Layer D in a reception side collects the packets transmitted from the transmission side to configure the collected packets to the package of Layer E1. A receiver recognizes elements of the content within the package, a relation between the elements of the content, and information on construction of the elements of the content, to transfer the recognized information to a content element relation/construction processor and a content element processor. The content relation/construction processor transfers the respective elements for the proper reproduction of the entire content to the content element processor, and the content element processor controls elements to be reproduced at a set time and displayed at a set position on a screen.
However, a conventional Layer E2 technique provides only the AU itself or information on a processing time for the AU reproduction, e.g., a Decoding Time Stamp (DTS) or a Composition Time Stamp (CTS) and a Random Access Point (RAP). Accordingly, the utilization of the conventional Layer E2 technique is limited.